1. Field of the Invention
The invention relates in general to a scanning device or auxiliary device of the scanning device, and more particularly to a sheet-fed scanning device with cleaning mechanism for cleaning the fed-in document in a sheet-fed scanning device.
2. Description of the Related Art
Scanner is a widely used electronic input device. Critical parts of a scanner include a scanning module and a mechanic transmission portion. A sheet-fed scanner whose mechanic transmission portion has simple structure embodies the design of a small-sized portable scanning input device. The sheet-fed scanner normally adopts a contact image sensor (CIS) being still with respect to the body of the scanner, and the fed-in document is scanned by way of being moved with respect to the scanner body. Such way of scanning is applicable to a small-sized portable scanner in scanning a small-sized document such as photo, receipt, business card and other types of cards.
FIG. 1 shows a cross-sectional structure of a generally known portable scanner 100 when scanning a fed-in document. The portable scanner performs scanning with a CIS scanning module 130 being still with respect to the scanner body 110. A fed-in document 160 is placed on a document supporter 170 of a fed-in document entrance 120. The fed-in document 160 is conveyed by a mechanic transmission portion in the direction of an arrow illustrated in FIG. 1. The CIS scanning module 130 fixed inside the scanner body 110 is located above the fed-in document 160. The fed-in document 160 is driven by a sheet-feeding roller 140 of a document conveying mechanism. During the process of scanning, the fed-in document 160 enters the scanner via the fed-in document entrance 120 and is outputted from the fed-in document exit 150. The CIS scanning module 130 obtains a scanned data of the fed-in document 160 through the glass window 131. The portable scanner 100 is used for scanning many different types of documents, which inevitably have dust, liquid or other adhesive substances attached thereon. Let the scanned document be exemplified by a photo. Due to the adhesion characteristics of the surface of the scanned photo, it is very likely that the dust or the adhesive substances are carried to the surface of the glass window 131 of the CIS scanning module together with the fed-in photo during the scanning process. The dust or the adhesive substances that are attached or adhered onto the glass window 131 are hard to be removed. The glass window is a critical element with which the scanner obtains a scanned image. If the dust or the adhesive substances are attached or adhered onto the glass window, the scanning module will be beclouded, and the part of the fed-in document corresponding to the beclouded part will not be precisely scanned or will be scanned as a peculiar strip. As the scanning module is fixed on the scanner body, the glass window is hard to be cleaned. Meanwhile, the dust or the adhesive substances are also very likely to be attached or adhered on the feeding roller that drives the fed-in document, and further affect the normal operation of the rollers.
In order to remove the dust or the attached substances from the fed-in document, to improve scanning quality and to maintain the cleanness of the scanning module and the glass window, according to modern technology, a cleaning member parallel to the fed-in document is installed on the document supporter for cleaning the dust or the attached substances by means of surface friction which occurs between the cleaning member and the fed-in document. However, the above mechanism design has many defects. Firstly, the cleaning member is disposed at one side of the to-be-scanned surface and is hard to be fixed. Secondly, if the surface friction occurring between the cleaning member and the fed-in document is larger, the fed-in document will encounter a large resistance when the fed-in document is being fed in, and the scanning speed of the scanning module will lose its stability. As a result, problems such as extension and distortion in the scanned image will occur. Also, if the frictional resistance is too large, the surface of a dedicate fed-in document such as photo may be scratched. To the worse, if the pulling force between the feeding roller and the cleaning member is too large, the fed-in document may even be damaged or torn apart. On the other hand, as the cleaning member must be fixed, the dust and impurities once being attached or adhered onto the cleaning end of the cleaning member are hard to be cleaned. The dust and impurities may even be consolidated as big pellets. If the pellets come off the cleaning end and are carried to the glass window of the scanning element together with the fed-in document, severe scanning defects would occur.